The present invention relates to an improved punch assembly for use especially with high speed punching machines and a related method for prolonging the useful life of the punch assembly.
By way of background, in high speed turret punching machines, it is necessary to maintain the top of the punch assembly as close to the ram as possible. In addition, it is a matter of good practice to maintain the extreme bottom end of the punch member as flush with the bottom of the punch guide as possible. However, after a period of use, the punch member is sharpened by grinding the end thereof. This causes the sharpened end to lose its flush relationship with the end of the punch guide, thereby requiring a longer punching stroke of the machine with the attendant loss of time, considering that modern turret punching machines operate at the rate of approximately 200 strokes per minute. In addition, there is the added disadvantage that the longer stroke causes greater compression of the stripper spring, which in turn shortens its life because of the greater amount of flexing to which it is subjected.
In the past the foregoing problem was solved after a fashion by the use of a reversible split ring punch retainer member having a lip on one side thereof. The split ring punch retainer member is essentially located between the stripper spring and a fixed shoulder on the punch member. When the punch is new, that is before it has been sharpened, the side of the split ring punch retainer which does not have the lip bears against the shoulder on the punch member, and the lip is received in an enlarged bore in the split ring punch retainer. After the punch has been sharpened, the split ring punch retainer is demounted from the punch and is reversed so that the lip takes up the distance which has been taken off of the punch member by sharpening. However, this construction is deficient in that it requires disassembly of the punch assembly in order to bring the lip into operative position, and this is a rather inefficient and cumbersome procedure. In addition, the lip is very fragile and cannot take sustained punching activity. It is with overcoming the foregoing deficiencies of the prior punching assemblies that the present invention is concerned.